Across his two seasons with Sebastian Vettel as his team-mate, Leclerc out-qualified the four-time F1 champion by a score of 25-13, and that after the German had taken a six-one lead.
Following the arrival of Sainz as his new team-mate, Leclerc finished over half-a-second ahead of the Spanish driver in the first qualifying session of this year in Bahrain.
Leclerc was then three-tenths of a second clear in Q2 in Imola where Sainz failed to make the top-10 shoot-out.
In Portimão, however, it was Leclerc's turn to struggle as the Monégasque finished 0.3secs down and three places behind fifth-on-the-grid Sainz.
Asked whether Sainz had discovered 'a magic bullet' in qualifying, given Leclerc has often extracted performance from his car that had previously appeared not to be within it, sporting director Laurent Mekies said: "It’s not a magic bullet.
"It’s just hard work after hard work after hard work and hundredths of seconds of lap time that go one after the other as you build up the relationship, and that’s what it is.
"It’s nothing to do with magic bullets, only the hard work he has done now. It was very tricky conditions with the wind and tyres in qualifying [in Portugal] and he did very well with his team to get there."
Assessing Leclerc's qualifying performances overall, Mekies added: "What we see very often is that Charles has a kind of magic when it comes to qualifying.
"We saw that last year and this, so he has this capacity to find the extra few tenths [of a second] that he didn’t know where they were in our car. He does that on a regular basis. It’s nearly a normal business for him to do that
"I think [in Portugal] he was a bit less comfortable with the car.
"With Carlos, all his qualifying has been close, maybe not at that small magic level but he has been close and [in Portugal] Charles was not exactly able to use that and fortunately Carlos was able to step in."
Mekies is relieved that for now when one driver has on off-day in qualifying the other is able to perform and salvage the situation.
"For us, as a team, it’s a good demonstration of how important it is to have such a strong relationship between our drivers in this situation," added Mekies.
"When you have one not as comfortable as usual, boom, the other guy is there because both of them are very close to each other."
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